Dynamic Cable Assignment On Gigabit Infrastructure

ABSTRACT

A method and corresponding network interface device for communicating between devices connected to a LAN includes attempting to communicate between the network devices over an initial subset of the network media wires. If the communication fails, a subsequent subset of media wires is selected. The wires of this subsequent subset differ from the wires of the initial subset. If the attempted communication succeeds, the current subset of network media wires is used as the media over which subsequent network data is transmitted. Attempting to communicate over the media may include sending an initialization sequence such as an Ethernet Auto-negotiate sequence. In one embodiment, the network media is implemented as 8 wires of CAT 5 cabling suitable for use with a Gigabit Ethernet. In this embodiment, any subsequent subsets of the network media wires may consist of 4 of the 8 wires over which 100 Mbps Ethernet operation may occur.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of and claims priorityfrom U.S. patent application Ser. No. 10/320,885, filed on Dec. 17,2002.

BACKGROUND

1. Field of the Present Invention

The present invention generally relates to the field of data processingnetworks and more particularly to Ethernet networks employing twistedpair cabling such as CAT 5, CAT 5e, and CAT 6 cabling.

2. History of Related Art

In the field of data processing local area networks (LANs), thetransistor from 10/100 Megabits/second (Mbps) systems to 1000 Mbps(Gigabit) systems is well underway. The installed base of 10/100Ethernet systems was largely implemented with Category 5 (CAT 5),twisted pair cabling as specified by ANSI/EIA (American NationalStandards Institute/Electronic Industries Association) Standard 568.Standard 568 specifies the cable material as well as the types ofconnectors and junction blocks to be used in order to guarantee the datarate associated with the category. Originally, 100 Mbps Ethernet systemsused 4 twisted pairs (8 wires) of which 4 wires were terminated toground. More recently, 100 Mbps Ethernet typically employ improveddrivers that eliminate the need for the 4 ground wires. Gigabit Ethernetcan also be installed on CAT 5 systems having 4 twisted-pairs althoughall 8 wires are needed. Thus, at the physical layer, there issubstantially no difference between Gigabit Ethernet systems employingCAT 5 cabling and many 100 Mbps systems. It would be desirable toimplement an Ethernet system that took advantage of this hardwarecommonality to improve the availability or reliability of Gigabitinstallations.

SUMMARY OF THE INVENTION

The problems identified above are in large part addressed by a methodand corresponding network interface device for communicating betweendevices connected to a LAN. The novel method includes attempting tocommunicate between the network devices over an initial subset of thenetwork media wires. If the communication fails, a subsequent subset ofmedia wires is selected. The wires of this subsequent subset differ fromthe wires of initial subset. If the attempted communication succeeds,the current subset of network media wires is used as the media overwhich subsequent network data is transmitted. Attempting to communicateover the media may include sending an initialization sequence such as anEthernet Auto-negotiate sequence. In one embodiment, the network mediais implemented as 8 wires of CAT 5 cabling suitable for use with aGigabit Ethernet LAN. In this embodiment, any subsequent subsets of thenetwork media wires may consists of 4 of the 8 wires over which 100 MbpsEthernet operation may occur.

A network interface device according to the present invention mayinclude a processor having access to random access memory (RAM) and readonly storage (ROS) and configured to produce a set of processor signals.A host interface unit (HIFU) of the network interface device includesbuffers and logic enabling communication with the host device. A mediainterface unit (MIFU) receives the set of processor signals and producesa resulting set of output signals that are provided to a LAN media. Thenetwork interface device is enabled to reroute at least a portion of theprocessor signals upon determining that communication over the media hasfailed. The rerouting causes a subset of the MIFU output signals to beprovided to a functional subset of media wires. In one embodiment, thenetwork interface device is a Gigabit Ethernet network device configuredto use 8 wires of a CAT 5 media. In this embodiment, the networkinterface device is configured, upon determining that the communicationhas failed, to reroute the processor signals to a subset of 4 functionalwires and to operate as a 100 Mbps network interface device using these4 wires thereby providing network communication functionality in theface of a partial network media failure.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to theaccompanying drawings in which:

FIG. 1 is a block diagram of selected elements of a network according toone embodiment of the present invention;

FIG. 2 is a block diagram of selected elements of a network interfacecard suitable for use in the network of FIG. 1;

FIG. 3 is a diagram of selected elements of a network according to oneembodiment of the invention;

FIG. 4 is a conceptual depiction of a table suitable for use in a NICemploying logical signal re-routing according to one embodiment of theinvention; and

FIG. 5 is a flow diagram of a method of configuring a network mediaaccording to one embodiment of the invention.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that the drawings and detaileddescription presented herein are not intended to limit the invention tothe particular embodiment disclosed, but on the contrary, the intentionis to cover all modifications, equivalents, and alternatives fallingwithin the spirit and scope of the present invention as defined by theappended claims.

DETAILED DESCRIPTION OF THE INVENTION

Generally speaking, the present invention contemplates the ability toimprove reliability and availability of a network such as an EthernetLAN by detecting when one or more of the signal cables within thenetwork's physical media is defective and rerouting signals to takeadvantage of unused signals. If the system suspects that a signal wireis defective, the signal corresponding to the defective wire isre-routed to an available wire. In this manner, the inventioncontemplates a network interface device employing the concept of alogical signal that is not necessarily tied to a particular physicalwire within the media. If the system incorporates the ability to operatein an environment that does not require all of the media's signal wires,the system can maintain availability if one or more of the wires becomesdefective by using available and functioning wires within the media toimplement the physical media. If, for example, a particular LAN is a CAT5, Gigabit enabled system employing 4 twisted-pairs of signal cables andone of the signal cables becomes defective, the system could transitionto a 2 twisted pair compatible environment, such as a 100 Mbps system,by logically routing one of the 100 Mbps signals to one of the fourwires that represent “spares” in a 100 Mbps system. In this manner, theinvention facilitates communication between devices on a network byattempting initially to communicate over a first subset of wires withinthe media. If the initial communication fails, a subsequent subset ofwires (different than the initial subset of wires) is selected toimplement the media and a subsequent communication is attempted. If thissubsequent communication succeeds, the currently selected subset ofwires is then used as the network media over which network data can betransmitted between the network devices. If the subsequent communicationfails, a new subset of wires is chosen and tried. This process isrepeated until the communication is successful or until there are nomore suitable subsets of wires over which the communication can beattempted, in which case an interrupt is issued.

Turning now to the drawings, FIG. 1 is a simplified block diagram ofselected components of the data processing network 100 according to oneembodiment of the present invention. In the depicted embodiment, network100 is an example of a LAN in which one or more data processing devices102 are connected to a switch 104. Data processing device 102 mayinclude servers, storage devices, desktop machines, network computers,data terminals, and the like. Switch 104 may comprise a router or thelike to which multiple devices 102 are connected.

Network 100 employs a physical medium 103 to connect device(s) 102 toswitch 104. In the preferred embodiment of the invention, physicalmedium 103 includes 4-pair (8 wire) CAT 5 cabling suitable for use in1000, 100, and 10 Mbps Ethernet systems as specified in IEEE 802.3. Suchsystems include 10BaseT4, 100BaseT4, and Gigabit Ethernet systems.

The depicted embodiment of network 100 includes a gateway and firewallunit 106 that connected to switch 104. Unit 106 is suitable forconnecting network 100 to an external network 108 such as the Internet.Although unit 106 is illustrated as a single unit, it will beappreciated that unit 106 may include two or more physically distinctdevices.

Device 102 and switch 104 are both depicted as including a networkinterface device (referred to herein as a NIC) 120. NIC 120 may beimplemented as an adapter card that connects to a processing board ormotherboard. Alternatively, NIC 120 may be integrated onto themotherboard or integrated within a processor itself. NIC 120 isconfigured to enable a processor on the corresponding device tocommunicate with external devices over the physical medium 103.

Referring now to FIG. 2, selected elements of a NIC 120 according to thepresent invention are shown to emphasize features of the invention. NIC120 is suitable for use as the network interface for device 102 andswitch 104. Although the network interface for device 102 and switch 104may have unique elements, the elements depicted in FIG. 2 are common toeach and are sufficient to enable NIC 120 to communicate informationbetween the host (device 102 or switch 104) in accordance with theteachings of the present invention. NIC 120 includes hardware, software,or a combination of the two, that enables the NIC to convert digitalinformation to a set of signals suitable for transmission over medium103.

In the depicted embodiment, NIC 120 includes a processor 130, randomaccess memory (RAM) 132, Read-only storage (ROS) 134, a host interfaceunit (HIFU) 136, and a media interface unit (MIFU) 138. Processor 130 islikely implemented with an embedded controller such as a Series 403PowerPC® embedded controller from IBM Corporation. Alternatively,processor 130 could be implemented with a general purpose CISC or RISCprocessor or DSP processor. It is also possible that NIC 120 could beembedded within a single chip that integrates any or all of processor130, RAM 132, ROS 134, HIFU 136, and MIFU 138. RAM 132 is connected toprocessor 130 and provides a scratch memory area for the processor. ROS134 is typically programmed or manufactured to store a sequence orsequences of instructions executable by processor 130. The HIFU 136typically includes buffers and associated logic that enables NIC 120 tocommunicate with its host, whether it is device 102, switch 104, oranother host.

The depicted embodiment of MIFU 138 is configured to receive digitalinformation provided by processor 130 and to convert or format thecorresponding information for transmission over the network media 103.In an Ethernet embodiment of network 100, the physical layer includesvarious sublayers that are implemented within NIC 120 and MIFU 138.Eight bit data chunks referred to as frames are transmitted from a mediaaccess control (MAC) layer, to a physical coding sublayer (PCS) througha Gigabit Media Independent Interface (GMII). MIFU 138 converts theinformation received from the GMII into signals suitable fortransmission over media 103. In one implementation, MIFU 138 employs aPulse Amplitude Modulation 5 (PAM 5) to encode the frames. PAM 5encoding resolves each of the media wires into one of five data levels(−1.0, −0.5, 0, 0.5, and 1.0) enabling the encoding of a large number ofsignals. In a four wire media, for example, PAM 5 encoding enables thegeneration of 5⁴ or 625 potential codes, which is more than sufficientto encode 8-bit frames.

In one embodiment, processor 130 generates processor signals that areprovided to the wires in media 103 through the intervening MIFU 138. Thesignals produced on media 103 reflect the correspondence between theprocessor signals, the signals output from MIFU 138, and physical mediasignal wires. If a device 102 within the system determines that itsconnection is non-functional, NIC 120 may logically re-route its outputsby altering the correspondence between the processor signals andphysical media wires. If NIC 120 is able to find a minimum number offunctional signal wires in media 103, NIC 120 may reroute the signals itproduces to the functional signal wires thereby enabling the system tocontinue operation, even if at a reduced data rate.

Referring now to FIG. 3 and FIG. 4, selected elements of the network 100are shown to emphasize aspects of the invention. In the illustration,network media 103 is shown as including 8 wires configured as 4 twistedpairs identified as PR 1, PR 2, PR 3, and PR 4. These eight wires arecommonly terminated at a suitable connector such as the depicted RJ 45connector 140. Connector 140 receives its eight signals from the eightsignals 151-158 produced by MIFU 138. MIFU 138 generates signals 151-158based upon the state of eight signals 141-148 (processor signals)produced by processor 130. One embodiment of NIC 120 maintains a table150 in RAM 132 that defines the correspondence between logical outputpins and physical output pins of processor 130. Table 150 may also beimplemented with a special or general purpose register. Processor 130includes the ability to produce any possible correspondence between itslogical pins such that any logical pins may be assigned to any physicalpin. If NIC 120 determines that one or more signal wires in media 103 isnon-functional, NIC 120 may reconfigure the logical to physical pincorrespondence to re-route signals to a set of functional signal wiresin media 103.

Portions of the invention may be implemented as a set of computerexecutable instructions (software). The software may be stored on acomputer readable medium, including, in this example, ROS 134 and RAM132 of NIC 120. ROS 134 may be implemented with a ROM, flash memorydevice, or any other suitable non-volatile storage device. RAM 132 istypically implemented with one or more DRAM modules.

Referring now to FIG. 5, a flow diagram illustrating a method 170 ofimplementing a network media according to one embodiment of theinvention is presented. Initially, an attempt to communicate betweennetwork devices is made by first sending some form of initializationsequence over the network media over an initial subset of wires withinthe media. In the depicted embodiment, the initialization sequenceincludes an Ethernet Auto-negotiation sequence as indicated in block172. Most Ethernet 100 Mbps adapters and all Ethernet Gig Adaptersincorporate an Auto-negotiation feature that enables the adapter tocommunicate with slower (10 Mbps) adapters. Auto-negotiation is definedin Clause 28 of the 1998 edition of IEEE Standard (Std) 802.3. During anEthernet Auto-negotiation sequence, two devices determine the highestlevel of service at which both ends of the connection can operate. Thelevels of services are prioritized according to a predetermineddefinition. Initially, both ends of the connection configure themselvesaccording to the lowest priority level of service (typically 10BaseT).The systems then attempt to negotiate for a mutually attainable higherlevel of service using the Auto-negotiation procedure.

One embodiment of the present invention leverages the Auto-negotiationfunctionality of the large installed base of Ethernet adapters todetermine if network media 103 is functional. If media 103 is determinedto be non-functional, the invention attempts to maintain networkfunctionality by re-routing signals to a functional set of wires. Morespecifically, one embodiment of the invention relies on the Fast LinkPulse (FLP) generated by Ethernet adapters at the start of theAuto-negotiation process to verify the integrity of the media.

Fast Link Pulse (FLP) signals are a modified version of the Normal LinkPulse (NLP) signals used for verifying link integrity, as defined in theoriginal 10BaseT specifications. FLP signals are generated automaticallyat power-up, or may be selected manually through a management interfaceto an Auto-negotiation device such as NIC 120. Like the original NLP,FLP signals take place during idle times on the network link and do notinterfere with normal traffic. FLP signals are conventionally used tosend information about device capabilities. The Auto-negotiationprotocol contains rules for device configuration based on thisinformation that enables the NICs 120 in switch 104 and device 102 toautomatically negotiate and configure themselves to use the highestlevel of service.

Because Auto-negotiation was originally specified for 100 Mbps adaptersthat may have been installed on 2 pair cabling systems, the FLP signalsare restricted to 2-pairs of wires even on systems (such as Gigabitsystems) employing 4 pair cabling. If one of the four wires in the 2pairs used to send the FLP signals is non-functional (open, shorted toground, shorted to Vdd, and so forth), the Auto-negotiation will notcomplete successfully. To detect and respond to this condition, thedepicted embodiment of the present invention monitors for a timeoutcondition (block 174) after initiating the Auto-negotiation sequence.

If a time out is detected in block 174, the present invention assumesthat one of the four original FLP wires is non-functional. In responseto this determination, the depicted embodiment of method 170 thensequences through the set of possible logical/physical pin permutationsuntil a setting is detected that results in the successful transmissionof the FLP signals. More specifically, upon detecting a timeoutcondition in block 174, method 170 then determines (block 176) whetherall of the possible media configurations or subsets have been exhausted.If not, NIC 120 reroutes (block 178) its logical-to-physical pinassignments to the next logically sequential combination andre-initiates the Auto-negotiation process (block 178). If a timeoutoccurs using the newest combination, the next logically sequentialcombination is attempted and so forth until all combinations have beenattempted. If all combinations of logical/physical pin assignments haveused without successfully resulting in the transmission of an FLP, aninterrupt is issued (block 180) and the process terminates with a fatalerror condition. If a timeout does not occur, implying that theAuto-negotiation sequence completed successfully, the network link isestablished at the negotiated level of service using the physical signalwires that were determined to be functional. In this manner, theinvention enables any connection employing 4-pair CAT 5 wiring tocontinue operation at speeds of up to 100 Mbps even if 50% of themedia's signal wires are non-functional. This elegant solution thusprovides a significant level of fault tolerance into the network at aminimal cost.

The process of using different logical/physical pin combinations asdescribed above effectively re-routes the FLP signals onto differentcombinations of wires within media 103. If any four of the wires inmedia 103 are functional, the FLP handshake sequence will eventuallycomplete normally. In one embodiment, the switch 104 is configured asthe receiver of the FLP signals while the device 102 is the sender.Switch 104 may be configured to read all 8 wires. In a typicalimplementation, the wires in media 103 are tied to a voltage source (Vssor Vdd) through a high impedance element such as a suitable resistor. Insuch an implementation, an open or otherwise floating wire in media 103will be tied to a static voltage level. Since the FLP signals “wiggle”each of the corresponding signal wires, it will be apparent to switch104 which wire(s) are bad. Upon discovering 4 functional wires, theswitch can re-route the 4 active bits onto the four functional wires.All subsequent packet transfers can then occur over the 4 functioningwires.

It will be apparent to those skilled in the art having the benefit ofthis disclosure that the present invention contemplates a method andsystem for using and configuring a network media. It is understood thatthe form of the invention shown and described in the detaileddescription and the drawings are to be taken merely as presentlypreferred examples. It is intended that the following claims beinterpreted broadly to embrace all the variations of the preferredembodiments disclosed.

1. A method of communicating between first and second devices connectedby a network media comprising a set of wires, the method comprising:attempting to communicate between the first and second network devicesover a current subset of the network media wires; responsive todetermining that the attempted communication failed, selecting asubsequent subset of media wires wherein the network media wires withinsaid subsequent subset and said current subset differ in at least oneelement; and responsive to determining that the attempted communicationsucceeded, using at least the current subset of network media wires asthe media over which subsequent network data is transmitted between thefirst and second devices.
 2. The method of claim 1, wherein attemptingto communicate over a network media comprises sending an initializationsequence responsive to connecting the first and second devices to thenetwork media.
 3. The method of claim 2, wherein sending aninitialization sequence comprises initiating an Auto-negotiationsequence between the network devices.
 4. The method of claim 1, whereinthe network media comprises 8 wires of CAT 5 cabling and wherein thecurrent and any subsequent subsets of the network media wires consistsof 4 of the 8 wires.
 5. The method of claim 1, wherein determining thatthe attempted communication failed comprises determining that apredetermined time period has elapsed.
 6. The method of claim 1, whereinusing the current subset of network media wires further comprises,responsive to successfully communicating between devices on a firstattempt, using all of the network media wires as the media over whichsubsequent network data is transmitted.
 7. The method of claim 6,further comprising, responsive to determining that transmission ofnetwork data over all of the media wires is unsuccessful, selecting thecurrent subset of network media wires as the network medium.
 8. Anetwork interface device suitable for connecting a host device to alocal area network (LAN), comprising: a processor having access torandom access memory (RAM) and read only storage (ROS) and configured toproduce a set of processor signals; a host interface unit (HIFU)including buffers and logic enabling communication with the host device;a media interface unit (MIFU) configured to receive the set of processorsignals and to produce a set of output signals based thereon that areprovided to a LAN media; and means for rerouting at least a portion ofthe processor signals, responsive to determining that communication overthe media has failed, wherein the rerouting causes a subset of the MIFUoutput signals to be provided to a functional subset of media wires. 9.The network interface device of claim 8, further comprising means forsending an initialization sequence over at least a subset of the wiresin the media.
 10. The network interface device of claim 9, wherein themeans for sending the initialization sequence comprises means forinitiating an Auto-negotiation sequence between the network devices. 11.The network interface device of claim 8, wherein the network mediacomprises 8 wires of CAT 5 cabling and wherein the functional subset ofwires consists of 4 of the 8 wires.
 12. The network interface device ofclaim 8, wherein determining that the communication failed comprisesdetermining that a predetermined time period has elapsed withoutsuccessful completion of a communication.
 13. The network interfacedevice of claim 8, wherein responsive to successfully communicating overthe media on a first attempt, the network interface is furtherconfigured to use all of the network media wires as the media over whichsubsequent network data is transmitted.
 14. The network interface deviceof claim 13, wherein the network interface device is furthercharacterized as a Gigabit Ethernet network interface device.
 15. Thenetwork interface device of claim 14, wherein upon determining that thecommunication failed, the network interface device reroutes theprocessor signals to a subset of 4 wires and the network interfacedevice operates as a 100 Mbps network interface device.
 16. A networkinterface device suitable for connecting a data processing system to alocal area network (LAN), comprising: means for attempting tocommunicate with another device connected to the LAN over a currentsubset of the network media wires; means for determining that theattempted communication failed and, responsive thereto, selecting asubsequent subset of media wires wherein the network media wires withinsaid subsequent subset and said current subset differ in at least oneelement; and means for determining that the attempted communicationsucceeded and, responsive thereto, using at least the current subset ofnetwork media wires as the media over which subsequent network data istransmitted between the first and second devices.
 17. The networkinterface device of claim 16, wherein the means for attempting tocommunicate over a network media comprises means for sending aninitialization sequence responsive to connecting the first and seconddevices to the network media.
 18. The network interface device of claim17, wherein the means for sending an initialization sequence comprisesmeans for initiating an Auto-negotiation sequence between the networkdevices.
 19. The network interface device of claim 16, wherein thenetwork media comprises 8 wires and wherein the current and anysubsequent subsets of the network media wires consists of 4 wires. 20.The network interface device of claim 16, wherein means for determiningthat the attempted communication failed comprises means for determiningthat a predetermined time period has elapsed.
 21. The network interfacedevice of claim 16, wherein the means for using the current subset ofnetwork media wires further comprises, responsive to successfullycommunicating between devices on a first attempt, means for using all ofthe network media wires as the media over which subsequent network datais transmitted.
 22. The network interface device of claim 21, furthercomprising, means for selecting the current subset of network mediawires as the network medium responsive to determining that transmissionof network data over all of the media wires is unsuccessful.